1. Field of the Invention
The present invention relates generally to medical devices and, in particular, to medical catheters having fibrous reinforcement layers, and improved methods for making the same.
2. Description of the Related Art
Almost all medical catheters have fibrous reinforcement in the wall of the catheter. Usually the reinforcement is in the form of individual filaments, such as wires or small fiber bundles. These filaments are usually braided. Braiding has the disadvantage that the size of the filament is limited (i.e., if the filament is very small it tends to break during the braiding process).
Filament winding is also used to make catheters, as described in the Applicant's prior U.S. Pat. No. 6,030,371. There are many advantages to constructing catheters with a filament wound reinforcement. For example, it is possible to wind very small filaments (e.g., 0.0005″ wires), which allows catheters to be constructed having a very small wall thickness.
FIGS. 1 to 4 show conventional process steps for making a filament wound catheter having a variable pitch. FIG. 1 shows a mandrel on which the catheter is formed; FIG. 2 shows the mandrel with a substrate placed thereon; and FIG. 3 shows the mandrel and substrate being rotated as a single filament is fed off a bobbin or spool and wrapped around the substrate. The single filament winding has a variable pitch over a length of the catheter, with the windings spaced closer together at a distal portion of the catheter as compared to a proximal portion of the catheter. FIG. 4 shows a cross section of the filament winding applied in a single pass over a length of the catheter. At the end of the single pass, the distal end of the filament either protrudes from the distal end of the substrate or is anchored thereto. The filament wound substrate shown in FIG. 4 is then coated with plastic (e.g., by applying a polymer in a particulate preform over the outer surface of the filament wound substrate, by laminating additional plastic tubes on top of the filament wound substrate, by extruding plastic over the filament wound substrate, or by applying the plastic as a molecular strand using electrostatic forces).
The catheter having a fibrous reinforcement formed by the process described above suffers from a number of disadvantages. For example, the filament tends to fray out of the wall or the distal end of the catheter and does not always remain intact during torque induced during use of the catheter. Thus, there is a need in the industry for an improved catheter having a fibrous reinforcement and methods of making the same.